Sunray captors, such as those described in Swiss Pat. No. 610 091, made up of a housing covered over with a single or double transparent plate in which a liquid circulates for conveying the trapped calories are well-known. The transparent plates are often ordinary panes of glass and are inconvenient in that they are extremely heavy. Consequently special supports are necessary, particularly when they are to be placed on the roof of a house, since the framework must be strong enough in order to bear heavy loads.
In order to avoid these disadvantages, sunray captors have been made which are covered over with a sheet of synthetic material, transparent to infra-red rays, which is stretched across a frame, preferably of a light alloy. Nevertheless the existing metal profiles do not easily lend themselves to such an assembly and the manufacturers are obliqued to use complicated artificial means in order to insure the tightening of the sheet on its support.
French Pat. No. 2,334,067 describes a sunray captor in which the transparent component is a film of synthetic material which is fixed on a rigid frame by means of blocking elements comprising a U-shaped groove into which an inverted U-shaped profile (blocking profile) is fitted. This device serves the sole function of holding the end of the film. The inconveniences of this type of device would thus be obvious to one of ordinary skill in the art. They include the fact that the front of the blocking profile must be inserted into the U-shaped groove by force, i.e., the open end of the U which is provided in the supporting frame. However, during this insertion, no means are provided for holding the supple film in position. On the other hand, in order to secure the film which has previously been tightened by the operator, into a locked position, the blocking profile must be adjusted and the film must, during the positioning of the profile, be manually maintained in a stretched condition. Moreover, the precision with which these two elements cooperate with each other in order to serve in this capacity will determine how well the fiber is blocked into position, and the manufacture of same will therefore be relatively expensive.
French Pat. No. 1,432,172 describes a means of fixing a sheet of supple synthetic material into a U-shaped groove which is narrowed down at its opening, principally by blocking a folded part thereof inside the U-shaped groove. This folded part is created by inserting a cord and a cable in a hem which is formed at the end of the sheet. This folded part can also possibly be blocked by a separate complementary member which is also inserted into the U-shaped groove.
The blocking device of this French patent thus only ensures the statici function of holding the sheet in place, and in no way allows a dynamic tension to be exerted on the edges of the sheet, so as to ensure its tightness on a frame. Moreover, this fixing means also requires the preliminary manufacture of a hem, and the tightness of the sheet therefore depends exclusively on the unchangeable positon of this hem. This device is thus unsuitable for fixing a transparent sheet on a rigid frame of fixed dimensions.